Power amplifier module

ABSTRACT

A power amplifier module comprises a plurality of amplifier stages, each including a reference amplifier for emulating the operation of the amplifier. The current flowing to the base of a bipolar transistor that forms each reference amplifier depending on an input power level is detected, amplified, and supplied as base current of the transistor of the corresponding amplifier.

TECHNICAL FIELD

[0001] The present invention relates to a power amplifier, moduledesigned for a portable terminal unit used in a mobile communicationsystem. More specifically, the present invention is related to a poweramplifier module designed for a cellular telephone system requiring ahigh efficiency and high linearity.

BACKGROUND ART

[0002] As conventional techniques related to power amplifier modules,there are JP-A-7-154169 and U.S. Pat. No. 5,629,648.

[0003] Very recently, while mobile communication markets typically knownas cellular telephone systems are considerably expanded, newcommunication systems such as the broadband CDMA system and the EDGEsystem have been conducted. In such systems, high efficiencies and highlinearity of portable terminal units are required. In particular, as topower amplifier modules which constitute one of major electroniccomponents of terminal units, there is such a serious problem that thesecontradicting performance requirements are realized at the same time.Conventionally, many attempts have been made so as to solve thisproblem. As a typical example, in general, one control system has beenproposed. In this system, an input power level of a power amplifiermodule is detected, and then, an operation condition of a post-stageamplifier which constitutes the power amplifier module is controlled bythis signal. For instance, in a prior-investigated technical exampleshown in FIG. 3, a gate voltage of a transistor 111 which constitutes apost-stage amplifier 101 is controlled based upon a DC voltage obtainedby envelope-detecting and smoothing an output signal of a pre-stageamplifier 102 in a DC voltage generating circuit 103 which is arrangedby a directional coupling device 106, a detecting diode 107, and alow-pass filter 108. The DC voltage is increased/decreased in responseto a power level inputted into a terminal 104, namely, a gate voltage ofthe post-stage amplifier 101 is controlled in response to the inputpower level. Also, in a prior-investigated technical example shown inFIG. 4, a power supply current of a first amplifier 201 is detected by apower supply voltage control circuit 203, and a power supply voltagecorresponding to this current value is generated so as to control apower supply voltage of a second amplifier 202. Since the power supplycurrent of the first amplifier 201 is changed in correspondence with alevel of power inputted into a terminal 204, the power supply voltage ofthe second amplifier 202 is controlled in response to the input powerlevel.

[0004] In the above-explained prior-investigated technical example, theDC voltage generating circuit 103 is required in order toenvelope-detect and smooth the output power level of the pre-stageamplifier 102. However, since this DC voltage generating circuit 103must be separately provided with reference to the amplifiers 101 and102, there is such a problem that the stable characteristic of this DCvoltage generating circuit 103 can be continuously and hardly guaranteedwithout any adjustment with respect to variations of environmentconditions such as manufacturing deviation and ambient temperatures, andalso power supply voltages. Furthermore, since the DC voltage generatingcircuit 103 is constituted by such components having differentcharacteristics as the directional coupling device 106, the detectingdiode 107, and the low-pass filter 108, there is another problem thatthe DC voltage generating circuit 103, and the amplifiers 101, 102 canbe hardly formed in an integrated circuit.

[0005] In the prior-investigated technical example of FIG. 4, theDC-to-DC converter is required to be employed as the power supplyvoltage control circuit 203 for controlling the second amplifier 202.However, there are such problems that the use of such a DC-to-DCconverter may constitute a factor of impeding the integratingmanufacture of electronic components, and furthermore, the module ismade bulky as well as the manufacturing cost is increased.

[0006] Also, the circuit system disclosed in the above-described U.S.Pat. No. 5,629,648 corresponding to the prior art may be considered. Inthis circuit system, since the output of the reference transistor,namely, the voltage at the bias point corresponding to the base input ofthe main transistor is not substantially changed in connection with thechange in the input amplitudes, there is a problem that the output ofthe reference transistor can hardly give effectively influences toup/down of the operating point of the main transistor.

DISCLOSURE OF THE INVENTION

[0007] An object of the present invention is to solve the problems ofthe above-described prior art and also the problems of theabove-explained prior-investigated technical examples, and is to providea low-cost power amplifier module which owns a high efficiency and ahigh linear characteristic, and further, can be easily manufactured inan integrated circuit form.

[0008] To achieve the above-described object, a power amplifier module,according to the present invention, is featured by that a referenceamplifier is newly employed which simulates operations of respectivestages of amplifiers for constituting the power amplifier module, acurrent flowing through an input terminal of this reference amplifier inresponse to an input power level is detected/amplified, and then, thedetected/amplified current can be supplied as an input current of theabove-described amplifiers.

[0009] In the present invention, an input signal is supplied viaindividual capacitors to the reference amplifier and the respectivestage amplifiers. At this time, although the current responding to theinput power level flows through the input terminal of the referenceamplifier, no current flow through the input terminals of the respectivestage amplifiers. Therefore, if a DC component of the input current ofthe reference amplifier is detected and amplified, and thedetected/amplified DC component current is supplied to the inputterminals of the respective stage amplifiers, then the respective stageamplifiers commence high frequency operations. When the input powerlevel is increased, the input current of the reference amplifier isincreased, so that the input currents supplied to the respective stageamplifiers are also increased. Conversely, when the input power level islowered, the input current of the reference amplifier is decreased, sothat the input currents supplied to the respective stage amplifiers arealso decreased. In other words, since the operating point correspondingto the input power can be set, even when the small input power issupplied, a relatively high efficiency can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a diagram for showing one embodiment of the presentinvention.

[0011]FIG. 2 is a diagram for representing one embodiment of the presentinvention.

[0012]FIG. 3 is a diagram for indicating an example of theprior-investigated technique.

[0013]FIG. 4 is a diagram for indicating an example of theprior-investigated technique.

[0014]FIG. 5 is a diagram for representing manufacturing deviation ofone embodiment according to the present invention.

[0015]FIG. 6 is a diagram for showing a circuit arrangement of oneembodiment of the present invention.

[0016]FIG. 7 is a diagram for indicating a packaging condition of oneembodiment of the present invention.

[0017]FIG. 8 is a diagram for showing one embodiment of the presentinvention.

[0018]FIG. 9 is a diagram for showing one embodiment of the presentinvention.

[0019]FIG. 10 is a diagram for showing one embodiment of the presentinvention.

[0020]FIG. 11 is a diagram for representing a circuit arrangement of oneembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] In general, a power amplifier module is arranged by employingeither two stages or three stages of unit amplifiers. FIG. 1 representsan embodiment of unit amplifiers which constitute a power amplifiermodule according to the present invention. The unit amplifier of thisembodiment is constituted by an amplifier 1 for power-amplifying aninput signal, a reference amplifier 3, a DC current amplifier 3,input/output matching circuits 8 and 9, and also, coupling capacitors 6and 7. The reference amplifier 2 produces a DC component of an inputcurrent in correspondence with a level of input power. The DC currentamplifier 3 amplifies this DC current component, and then supplies thiscurrent-amplified DC component to the amplifier 1. In this case, in sucha case that a dimension ratio of a transistor 11 to another transistor12 is equal to n:1, which constitute both the amplifier 1 and thereference amplifier 2, a current amplification factor of the DC currentamplifier 3 is set to be larger than, or equal to “n.” The larger thiscurrent amplification factor is increased, the larger a distortionreducing effect achieved when a large output current is outputted isincreased. As a result, the current amplification factor is set in sucha manner that this current amplification factor is fitted to a targetvalue of reducing distortion at a design stage. In this embodiment,while both the reference amplifier 2 and the amplifier 1 are arranged insuch a way that the input/output matching circuits 8 and 9 are commonlyused by these amplifiers 2 and 1, the operation condition of theamplifier 1 is substantially equal to the operation condition of thereference amplifier 2, so that a high linear characteristic (highlinearity) may be obtained. Also, since the transistors 11 and 12 whichconstitute both the amplifier 1 and the reference amplifier 2 aremanufactured on the same chip, the linearity may be maintained even insuch a case that manufacturing deviation occurs and environmentconditions are changed. It should be noted that an Si bipolartransistor, GaAs-HBT, SiGe-HBT, and the like may be employed as thesetransistors 11 and 12.

[0022] Next, operations of the above-described embodiment will now bedescribed. A signal inputted from the terminal 4 is transferred via thecoupling capacitors 6 and 7 to the amplifier 1 and the referenceamplifier 2. The input signal is amplified by the reference amplifier 2.At this time, a DC component is produced in the input current of thisreference amplifier 2 because of a non-linear operation of thetransistor 12 which constitutes this reference amplifier 2. Since thisDC component is changed in response to a level of input power in anone-to-one correspondence, if this DC component is detected, then avalue of an input current which should be supplied to the amplifier 1can be grasped. Since the dimension of the transistor 11 is larger thanthe dimension of the transistor 12, the DC current detected by thereference amplifier 2 is amplified by the DC current amplifier 3, andthereafter, the amplified DC current is supplied by the DC currentamplifier 3 as an input current of the amplifier 1. When the current issupplied from the DC current amplifier 3, the amplifier 1 commences tobe operated. In an actual case, both the amplifier 2 start theiroperations at the substantially same time. The input current of theamplifier 1 is changed in a dynamic manner in response to the inputpower level by the above-described operation mechanism. When the inputpower level is high, this input current is increased, and the operatingpoint of the transistor 11 of the amplifier 1 is automatically set to behigh. As a result, the amplifier 1 can perform the power amplificationwith low distortion. Also, conversely, when the level of the input poweris low, the input current is decreased, and thus, the operating point ofthe transistor 11 of the amplifier 1 is lowered. As a result, uselesspower consumption can be reduced, and lowering of the power efficiencywithin the region where the input power level is low can be reduced.

[0023]FIG. 2(a) and FIG. 2(b) indicate an embodiment of both two stagesand three stages of power amplifier modules, respectively, which areconstituted by employing the unit amplifier shown in FIG. 1. Thetwo-stage power amplifier module is applied many times to a CDMA system,a PDC system, and the like, whereas the three-stage power amplifiermodule is applied many times to a GSM system, and the like. Signalsentered from a terminal 06 and another terminal 08 are sequentiallypower-amplified by either unit amplifiers 01, 02 or unit amplifiers 03,04, 05 in accordance with the operations explained in FIG. 1, and then,the power-amplified signals are outputted from a terminal 07, andanother terminal 09, respectively. Therefore, in FIG. 2(a) and FIG.2(b), since the electric power during operation is increased in thisorder of the unit amplifiers 01<02, and of the unit amplifiers 03<04<05,dimensions of transistors which constitute the unit amplifiers 01, 02,and the unit must be changed based upon power distributions which areallocated from the system specification. For instance, in post-stageamplifiers, especially, in final-stage amplifiers, since an electricpower level thereof becomes higher than an electric power level of apre-stage amplifier, such a transistor having the largest dimension isused. It should also be noted that input/output matching circuits amongthe respective unit amplifiers may be commonly used by way of a designchanged. In this alternative case, there is such a merit that the entireunit amplifier may be made compact. In the foregoing description, theinput current of the amplifier 1 is supplied by that the input currentof the reference amplifier 2 is supplied and amplified. Alternatively,instead of the input current of the reference amplifier 2, such acurrent which is obtained by detecting a power supply current to amplifythis detected power supply current may be supplied to the base of theamplifier 1. In this alternative case, instead of the base current ofthe transistor 12, the collector current thereof may be utilized.

[0024]FIG. 5 represents manufacturing deviation of a power amplifiermodule which was manufactured as a trial module based upon thisembodiment. Output power is 28 dBm. In this drawing, an abscissaindicates adjacent channel leak power corresponding to an index ofdistortion, and an ordinate shows a power adding efficiency, and themanufacturing deviation of the power amplifier module is indicated by anarea surrounded by a solid line. For the sake of easy comparisons,manufacturing deviation of the prior-investigated technical idea is alsoindicated in this drawing. An area indicated by a hatched line shows arange of a required specification. In the prior-investigated technicalidea, a good product acquiring rates of power amplifier modules whichmay satisfy the required specification is smaller than, or equal to 10%,whereas a good product acquiring ratio of the power amplifier moduleswhich may satisfy the required specification according to thisembodiment is improved up to 90%.

[0025]FIG. 6 indicates an embodied (exemplified) structure of a unitamplifier, according to an embodiment of the present invention. First, adescription will now be made of operations of this unit amplifier duringno signal. In this case, a collector current flowing through atransistor 12 is determined based upon a current supplied by a constantcurrent source 14 to a transistor 23, since both the transistor 12 andthe transistor 23 constitute a current mirror circuit. For example, if adimension ratio of the transistor 12 to the transistor 23 is selected tobe m:1, then a collector current of the transistor 12 becomes “m” timeslarger than the current supplied from the constant current source 14.When the collector current flows through the transistor 12, such acurrent defined by 1/current amplification factor will flow through thistransistor 12. This current flows via a transistor 24 into a transistor25, and then, is transferred to a transistor 26 which constitutes acurrent mirror circuit in connection with the transistor 25. Eventually,this current flowing through the transistor 26 is supplied as a basecurrent of a transistor 11, and may determine an operating point of thetransistor 11 under non-signal condition. In this case, both atransistor 27 and another transistor 28 constitute a current mirrorcircuit, and owns a current amplifying function capable of supplying alarge current which is required in such a case that the transistor 11 isconstituted by connecting, for example, 100 to 200 pieces of unittransistors in a parallel manner. In general, a current supplyingcapability of a PNP transistor is small, so that a dimension of this PNPtransistor becomes very large in order to supply a large current. As aresult, if the current amplifying function of the transistors 27 and 28is utilized, then the dimension of the transistor 26 can be made small.Next, a description will now be made of operations under such acondition that a signal is inputted to this unit amplifier. In thiscase, firstly, a signal is supplied via the coupling capacitors 6 and 7to the transistors 11 and 12. Since the transistor 12 owns thenon-linear characteristic, a DC component is produced in the basecurrent. This current having the DC component flows to the transistor 24via a high-frequency cut-off inductor 29. At this time, while a basecurrent corresponding to an input signal is not supplied to thetransistor 24, the current flowing through the transistor 24 is suppliedvia the transistors 25, 26, 27, and 28 in a manner similar to that whenno signal is entered, and thereafter, operation is commenced. Since thebase current value of the transistor 12 is changed in response to thelevel of the input power, the base current of the transistor 11 is alsochanged in response to this change in the input power level, and theoperating point when the signal is inputted is automatically set.

[0026] As the specific effect of this embodiment, a thermal run-awaysuppressing effect may be achieved. For instance, in the case thatoutput power of 36 dBm (4W) is required as in a power amplifier moduledesigned for the GSM system, a large-scaled transistor manufactured byconnecting 100 to 200 pieces of unit transistors in parallel manner isemployed as the transistor 11. When such a large-scaled transistor isarranged in high density within a chip, a thermal resistance isincreased. In the normal case, when a thermal resistance of a bipolartransistor is increased, a thermal run-away easily happens to occur, sothat there is a limitation in reducing of a chip area. While an easyoccurrence of a thermal run-away may depend upon a current supplyingcapability of a base bias circuit other than a thermal resistance, sincesuch a bias circuit having a large current supplying capability as aconstant voltage bias circuit is employed in a normal power amplifiermodule, a thermal run-away easily occurs. When high power is outputtedin a power amplifier module, a thermal run-away may readily occur. Inthis embodiment, however, since a current supplied to the transistor 11is limited by the input power level, the power amplifier module isarranged in such a manner that a thermal run-away can hardly occur. As aresult, in this embodiment, the chip area can be reduced, so that thepower amplifier module can be made compact.

[0027] It should also be noted that in the embodiment of FIG. 6, thetransistors 11, 12, 23, 24 may be constructed of GaAs-HBTs, and thetransistors 25, 26, 27, 28 may be constituted by either Si bipolartransistors or MOS transistors. Furthermore, the inductor 29 may bereplaced by either a resistor, or a series-connection of a resistor andan inductor.

[0028]FIG. 7 shows a component arrangement of the unit amplifieraccording to this embodiment. This drawing indicates such an examplethat both the amplifier 1 and the unit amplifier 2 shown in FIG. 6 areformed on a GaAs chip 16, and the DC current amplifier 3 shown in FIG. 6is formed on an Si chip 17 in an integrated circuit manner. The unitamplifier is constituted by these chips 16, 17, and the input/outputmatching circuits 8, 9 which are mounted on a module board. Aspreviously explained, in accordance with the present invention, themajor components of the unit amplifier are formed in the integratedcircuit form, so that a total number of electronic components thereofcan be reduced and the module can be made compact. Also, since thetransistor 11 and the transistor 12 are manufactured on the same chip,these transistors 11 and 12 may have a superior pair characteristic, andthus, may be operated under stable condition without being adverselyinfluenced by manufacturing deviation and environment variations. Itshould be understood that in order to effectively achieve theabove-described thermal run-away suppressing effect, as indicated inFIG. 7, the transistor 11 and the transistor 12 are manufactured bybeing separated from each other. AS a result, the transistor 12 can behardly influenced by adverse influences of heat of the transistor 11.

[0029]FIG. 8 shows a unit amplifier according to another embodiment ofthe present invention. This embodiment owns a different point that anoutput terminating circuit 18 is provided so as to terminate an outputof a reference amplifier 2 within the module, as compared with themodule of FIG. 1. Since the output of the reference amplifier 2 is cutout from the output terminal 5, an operation of the reference amplifier2 can be hardly influenced by a load. Since an operation current of theamplifier 1 is controlled by the reference amplifier 2, an operation ofthis amplifier 1 can also be hardly influenced by the load. As a directeffect of the above-explained operation, a load variation withstandingcharacteristic may be improved. In portable terminal units, destructionof antennas and contacts of these antennas to metals may occasionallyoccur when these portable terminal units are used, while these antennasconstitute loads of power amplifier modules. In such a case, sincematching conditions between the power amplifier modules and the antennasare broken, large standing waves are produced due to power reflections.Accordingly, the power amplifier modules may be readily destroyed. Inthis embodiment, even when reflection power occurred from an antenna isincreased, since the operation current of the amplifier 1 can be hardlychanged, it is possible to avoid the breakdown of the amplifier 1.

[0030]FIG. 9 indicates a unit amplifier according to another embodimentof the present invention. This embodiment owns such a differentstructure from that of FIG. 1. That is, an interstage matching circuit19 is provided, and an output of a reference amplifier 2 is connected toan input of an amplifier 1. This unit amplifier is arranged by atwo-stage amplifier, and a pre-stage amplifier may also function as areference amplifier. As a result, the reference amplifier need not beseparately provided, but a structure of a module can be made simple.Since the reference amplifier 2 is separated from the output terminal 5by the amplifier 1, there is such a merit that this unit amplifier canbe hardly influenced by the load variation similar to that of FIG. 8.

[0031]FIG. 10 indicates a unit amplifier related to a 3-stage poweramplifier module, according to another embodiment of the presentinvention. This embodiment owns a different point from that of FIG. 9.That is, both an amplifier 51 and an interstage matching circuit 52 areadditionally provided in the unit amplifier of FIG. 9. Similar to FIG.9, in this embodiment, while a first-stage amplifier is also operated asa reference amplifier 2, both a second-stage amplifier 51 and athird-stage amplifier 1 are controlled. In this case, since thereference amplifiers of the respective stages can be omitted, there is amerit that the structure of the unit amplifier can be made simple.

[0032]FIG. 11 indicates a unit amplifier according to another embodimentof the present invention. This embodiment is an application example inwhich the unit amplifier is applied to a field-effect transistor. Abasic structure of amplifier is identical to that of the embodimentshown in FIG. 9. Only such a point is different. That is, field-effecttransistors 21 and 22 are employed instead of the bipolar transistors 11and 12. In this embodiment, a DC component of a drain current of thefield-effect transistor 22 is detected. An output of a DC currentamplifier 3 is converted into a voltage by a transistor 34, and then,this converted voltage is applied to a gate of the field-effecttransistor 21. Such a technical point that an operating point isautomatically set in response to input power, and thus, alow-distortion/high-efficiency operation with superior reproducibilitycan be realized is similar to that of the above-described embodiment.

[0033] In accordance with the structures of the present invention, sincethe same sorts of transistors which constitute the reference amplifierand the respective stage amplifiers may be employed, these amplifierscan be readily formed in the integrated circuit, and an externalspecific circuit is no longer required. Also, since the referenceamplifier and the respective stage amplifiers are formed on the samechip in the integrated circuit form, this reference amplifier may beoperated in a substantially same manner to that of the respective stageamplifiers in the high frequency mode as well as the DC mode. As aconsequence, even when the manufacturing deviation of the transistors ispresent and the environment conditions are varied, the stablecharacteristic can be continuously obtained without any adjustment.Furthermore, since both the reference amplifier and the respective stageamplifiers can commonly use the matching circuits, a total number ofelectronic components can be reduced, and the power amplifier modulescan be made in small dimensions and also in low cost.

1. A power amplifier module comprising: a second amplifier, an inputcurrent of which is changed in response to an input power level; a DCcurrent amplifier for detecting a DC component of the input current ofsaid second amplifier and for amplifying the detected DC component ofthe input current; and a first amplifier to which the current amplifiedby said DC current amplifier is supplied as an input current.
 2. A poweramplifier module as claimed in claim 1 wherein: said power amplifiermodule is arranged in such a manner that a power supply current of saidsecond amplifier is detected and amplified by the DC current amplifier,and said amplified power supply current is supplied to an input terminalof said first amplifier.
 3. A power amplifier module comprising: thepower amplifier module recited in claim 1, or claim 2 as a unitamplifier; and wherein: said power amplifier module is constituted byconnecting plural stages of said unit amplifiers.
 4. A power amplifiermodule as claimed in claim 1, or claim 2 wherein: the input terminal ofsaid first amplifier is connected to an input terminal of said secondamplifier in an AC manner; and an output terminal of said firstamplifier is connected to an output terminal of said second amplifier inan AC manner.
 5. A power amplifier module as claimed in claim 1, orclaim 2 wherein: the input terminal of said first amplifier is connectedto an input terminal of said second amplifier in an AC manner; and onlyan output terminal of said second amplifier is internally terminated. 6.A power amplifier module as claimed in claim 1, or claim 2 wherein: theinput terminal of said first amplifier is connected to an outputterminal of said second amplifier in an AC manner.
 7. A power amplifiermodule as claimed in claim 1, or claim 2 wherein: an output terminal ofsaid second amplifier is connected to an input terminal of a thirdamplifier in an AC manner; an output terminal of said third amplifier isconnected to the input terminal of said first amplifier in an AC manner;and a current is supplied from said DC current amplifier to both theinput terminal of the first amplifier and the input terminal of thethird amplifier.
 8. A power amplifier module as claimed in claim 1, orclaim 2 wherein: said first amplifier, said second amplifier, and saidDC current amplifier are constructed of bipolar transistors.
 9. A poweramplifier module as claimed in claim 8 wherein: the bipolar transistorfor constituting said first amplifier and the bipolar transistor forconstituting said second amplifier are formed on the same chip in anintegrated circuit form.
 10. A power amplifier module as claimed inclaim 8 wherein: the bipolar transistors which constitute said firstamplifier and second amplifier, respectively, are made of eitherGaAs-HBTs or GaAs field-effect transistors; and said DC currentamplifier is made of either an Si bipolar transistor or an Sifield-effect transistor.
 11. A power amplifier module comprising: afirst amplifier using a first field-effect transistor; a secondamplifier using a second field-effect transistor; and a DC currentamplifier; wherein: said DC current amplifier detects and amplifies a DCcomponent of a drain current of said second field-effect transistor; anda gate voltage of said first field-effect transistor is controlled by anoutput current of said DC current amplifier.
 12. A power amplifiermodule as claimed in claim 11 wherein: said first field-effecttransistor and said second field-effect transistor are formed on thesame chip in an integral circuit form.